Abstract
Hydrogen adsorption on alumina-supported platinum has been reinvestigated in order to decide whether or not the “reversible” and “irreversible” forms of hydrogen adsorbed on platinum at room temperature can be detected by infrared spectroscopy.
The main conclusions of this work are: (i) the reversible hydrogen adsorption is dissociative and occurs for pressures higher than ca. 1 Torr; (ii) it is characterized by an infrared band at 2120 cm
−1; (iii) the “irreversible” form does not seem to be detected by infrared spectroscopy, in contrast with previous work which attributed an infrared band near 2040 cm
−1 to this kind of strong adsorption.
Our results have shown that carbonates, always present on alumina, decompose into CO
2 which is then dissociatively adsorbed on platinum. The Pt-CO species produced are responsible for a 2045
−1 band, which is shifted to higher frequencies for increasing coverage of the metallic surface by CO. Some considerations are advanced to explain why only one type of hydrogen adsorption is detected by infrared spectroscopy.